Which of the following materials is used in the manufacture of resistance grids to be used in the starters of large motors ?

Related Mcqs:

1. Which of the following problem arises in D.C. motors which are fed from thyristor bridge circuits ?

   A. Increased I R losses B. Increased core losses C. Poor commutation D. Change in motor parameters E. All of the above...

2. Which of the following in an application of D.C. motors?

   A. Traction B. Drives for process industry C. Battery driven vehicles D. Automatic control E. All of the above...

3. In induction motors, the length of air gap in kept as small as mechanically possible is order to have____________?

   A. low power factor B. high power factor C. high over load capacity D. any of the above...

4. In self cooled motors the cooling time constant is about ___________ than the heating time constant because cooling conditions are worse at standstill?

   A. 2 to 3 times greater B. 3 to 4 times greater C. 4 to 5 times greater D. none of the above...

5. For large power transformers, self oil cooled type or air blast type which of the following values of current density may be used?

   A. 1.0 to 1.2 A/mm2 B. 1.5 to 2.0 A/mm2 C. 2.2 to 3.2 A/mm2 D. 3.2 to 4.2 A/mm2...

6. Materials exhibiting zero value of resistivity are known as ____________ ?

   A. conductors B. semiconductors C. insulators D. superconductors...

7. The operation of a D.C. machine with large air gap lengths is comparatively_____________?

   A. quiet B. noisy C. either of the above D. none of the above...

8. D.C. machines designed with a large value of air gap length have_____________?

   A. worst, ventilation B. poor ventilation C. better ventilation D. none of the above...

9. A current density of __________ is ilsed for large power transformers with forced circulation of oil or with water cooling coils?

   A. 1.5 to 2.5 A/mm2 B. 3.5 to 4.5 A/mm2 C. 4.0 to 5.0 A/mm2 D. 5.4 to 6.2 A/mm2...

10. For 275 kV transformers, using cold rolled grain oriented steel, which of the following values of flux density may be used?

    A. 1.0 Wb/m2 B. 1.1 Wb/m2 C. 1.3 Wb/m2 D. 1.6 Wb/m2 E. None of the above...